Copy machines, printers, fax machines, scanners, multi-function devices, and other image forming apparatuses are common devices in business and homes. These image forming apparatuses and other sheet processing apparatuses perform sheet conveyance typically using a plurality of rollers. Each roller contacts and conveys a sheet via friction between the roller and the sheet. Depending on fault conditions, such as defects, roller degradation, low-quality sheets, abnormal temperatures, and so on, sheet conveyance may become excessively slow or fast, which may lead to jams or degradation of image processing (e.g., image forming) on the sheets. For that reason, it is desirable to detect problems early and perform maintenance as soon as possible.